Stack-forming synchronizer for a sorting machine



S. HENIG April 4, 1967 STACK-FORMING SYNCHRONIZER FOR A SORTING MACHINE 9 Sheets-Sheet 3 Filed April d, 1964 IN VENTOR ATTORNEY S. HENlG STACK-FORMING SYNCHRONIZER FOR A SORTING MACHINE 9 Sheets-Sheet L ATTORNEY April 4, 1967 Filed April G, 1964 S. HENIG April 4, 1967 9 Sheets-Sheet 5 Filed April G, 1964 1 fly MW Mr Y h om Nm FF n c m wm f o/f w ES AR [#5 Pm ##2, w MA 0R XL Y C M FC D 2 6 7 im .n n w m Z 2 A DMI YWW 1l.. LT O 6 d 8l FH d M WJG N l T/ UE., D0 ocN Y E04 TCU d m WC 6 A n um@ I+ T www n 5 B XEE M m d R O my wm 1H w m vv Qu C 5 d mm wx. md@

ATTORNEY April 4, 1967 s. HENIG 3,312,949

STACK-FORMING SYNCHRONIZER FOR A SORTING MACHINE Filed April 6, 1964 9 Sheets-Sheet ACTIVE UNLOAD CATEGOR/Es Fat'gl STACK LEADING EDGE STACK HDUO/AL STORE RETTMERS STORE RET/MER TRACK a TRA CRS TRA cu TRACK ONE BIT TW@ BIT ADVANCE ON /T ADVANCE Timm PMI wR/TE READ /32 READ wR/TE READ AMPL, N/Z 2E'LLTAMPL. AMPL. AMRLY AMPL.

R'ED WRITE /265 WRITE READ WRITE M, 28/

f" AMPL. T454 AMPL. AMPL. AMPL. AMPL.

NEXT ACTI Vb (JA/OAD CATEGORY ,Z7 CODE FROM /Of /73 SELECTOR 40J INVENTOR Seg/mow" Hel/T13 -.A QAM@ ATTORNEY April 4, 1967 s. HENTG 3,312,949

STACK-FORMING SYNGHRONIZER FOR A SORTING MACHINE Filed April 6, 1964 9 Sheets-Sheet 5 L E TTEI? CA 7560/? V SLOT ODD-EVEN cou/VT NUMBER STORE RET/MERS E TRA ERS TRAcR 2 TRACK IH TRACKS INPUT FROM ONE BIT Z Twig/T ADI/ANCE UN 55 Fe" ADVANCE I98 E f WRITE READI READ READ WRITE ARRL. AMELA AMRL. AMRL. AWIRLE, @LIE-2 272 45o IS7 222 Q?. -5I u j/ 27/ ma Isa READ READ WRITE WRITE WRITE READ AMRLE. H AMPL. AMPL. AMEL. AMRL. AMPLS """"76 IEE 269 ma Zl95--\- i-J" J I i I l /213 L I IDITDELAV INVENTOR .Seymour Heng BY I Fzg ATTORNEY S. HENIG April 4, 1967 9 Sheets-Sheet 6 Filed April 6, 1964 5 R o El, T NH4 7 N C O J E ma 5 6 v M WX 5, m m om e 5 0 T 0 l. C T G c... A .A l 8 e. 0M WF 0 (I4L CW 3 m IV no# of 7 Z w @w11 M 4 Wiki) R 7 M 00u ltkrlJ 5 M m Y6 a/o Z wml. l M r 0/ 1 3 T N0 M L W zu 2 A A 7 o @Mw .Km2 w ME F Mo 5 im C@ s ATTORNEY April 4, 1967 s. HENIG 3,312,949

STACK-FORMING SYNCHRCINIZER FOR A SORTING MACHINE Filed April 6, 1964 9 Sheets-Sheet Y SLOT NUMBER CATEGORY ODD-EVEN ACTIVE UNIOAO TRAcRs STORE TRACKO COUNT CA TEEORIES STORE TRACJKj STORE TRAlcg OHTRACTS um/O TRACKS f/d LEI? IO (i T T; vx 7 X @BITS CHAR@ 2O BITS-lfm m- 20 l 6BIT5 CHAR@ MRW CHAR@ CHAR@ L-hi @TRAO TRACKS 6 TRACKS @BITS CHAR #I V* i* INI H I I JI III 3I N X EZ 5o TRAIL @o BITS BIT ONE W10" sscTOR I T I I 1 I I I I 1 I I I 4o N 223 IE5 1*(,0 y 444 DIRECTION OF ROTA TION INVENTOR FT i 4 y eymow" Henry ATTORNEY S. HENIG April 4, 1967 STACK-FORMING SYNCHRONIZER FOR A SORTING MACHINE Filed April 6, 1964 9 Sheets-Sheet E MR ma ATTORNEY S. HENIG April 4, 1967 STACK-FORMING SYNCHHONIZER FOR A SORTING MACHINE Filed April 6, 1964 9 Sheets-Sheet Ylv www GSE GBQ w n@ .NRN

/NVE/vro/e Seymour` Hem'g ATTORNEY United States Patent O Commerce Filed Apr. 6, 1964, Ser. No. 357,846 12 Claims. (Cl. S40-172.5)

This invention relates to a stack-forming synchronizer and in particular to one that may be used in a sorting machine in which physically similar articles are deposited randomly into individual storage slots emplaced in a rack. In this type of machine, cach articles category information along with its storage location is filed in a memory. In order to sort, the memory is searched periodically for articles of like category which are then unloaded to a stack on a single conveyor belt. The belt is used for different categories during successive periods and emptied slots are immediately available for reuse by new articles of any category.

The present application is a continuation-impart of U.S. patent application Serial No. 289,761 entitled Sorting Machine Providing Self-Optimizing Inventory Reduction, which was tiled by Seymour Henig and Ervin C. Palasky on June 21, 1963.

The sorting machine, described in the above patent application, includes several stations, each having a rack containing a plurality of slots, each slot having a gate positioned above a common conveyor belt. An operator, reading the destination of .a letter to be sorted, operates a keyboard to record the related letter category code in the memory of a control computer. The letter is then dropped into the rst emp-ty slot and the number code of the slot is generated and stored in the memory.

Using the generated number code, the computer places the category code for each letter in relation to an identical number code prerecorded in a section of the memory whose arrangement is analogous to the slots physical locations in the rack. A running inventory with respect to categories is kept for the letters stored in the slots. Periodically, the computer makes a determination, premised on optimum inventory reduction, of the next category to ybe unloaded from the slots. The code of this category is then recorded in a section of the memory which retains a list of these active unload category codes of the stacks forming on the conveyor belt.

Cne embodiment of the present stack-forming synchronizer may be incorporated in a sorting machine of this type that uses a -drurn as the memory. The number of each slot in the rack is prerecorded in respective tracks on the drum and a letter category code may be written in tracks of the drum in alignment with the related slot number code. At the start of stack forming, each active unload category code is written on .a track of this drum in alignment with the number for slot l.

During one revolution of the memory drum, each active unload category code is read out and compared with the aligned letter category code, that is likewise read out of the memory drum. On the succeeding revolution of the drum, each active code is advanced to `a new alignment with that letter category code and slot number code written in respective tracks of the drum for the next one of the slots in the rack. Thus, on starting at the first slot, each active category code is compared with each letter category code written in the tracks of the memory drum for each of the slots in the rack. When an identity is found, the related slot number code is read out of the drum and applied to a decoding matrix to control the gate of a slot containing the letter related to the category being unloaded on the conveyor belt. The stack obtains its spread of letters from the cumulative difference pro- Frice vided by running the belt at a speed slightly less than one slot advance for each revolution of the memory drum.

In another embodiment of the present invention, the stack-forming synchronizer is provided with an arrangement that regulates the spacing of the letters in each stack. Since letter-spacing can have many ramifications, it is necessary to detine the kind of regulation that is being effected. Slot pitch is a convenient unit of linear measurement here, so the regulation is defined as follows: each letter added to the stack is positioned one-half slot ahead of the letter just previously added to the stack. This embodiment uses the same general method of active unload category code storage and traverse as the rst embodiment. However, the conveyor belt, instead of lagging, runs in step with the memory drum in the nominal exact ratio of one slot advance per revolution. Further, the odd-count additions are used to fill the half-slot places in a stack, and the even-count additions are used to fill the whole-slot places. (The odd-count additions are the first, third, fifth, etc. letters added to a stack, while the even-count additions are the second, fourth, sixth, etc. letters added to the stack.)

In the latter embodiment, a record is kept of the leading edge and another record is kept of the zero-letter position of the stack. Utilizing these records, a count of the number of letters in each stack and information relating to each completed stack on the conveyor belt is sent to the next stack-processing machine.

Accordingly, it is an object of the present invention to provide a stack-forming synchronizer for a sorting machine.

Another object is to provide a stack-forming synchronizer incorporating an arrangement for regulating the spacing of articles in each stack.

Another object is to provide a stack-forming synchronizer that generates a count of the articles in each stack and data concerning the position of each stack formed on a conveyor belt.

Other objects and advantages of the invention will become apparent from the following description of the annexed drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a block diagram of a sorting machine using the present invention;

FIG. 2 is a first embodiment of the present invention;

FIG. 3 is a block diagram showing the manner in which FIGS. 3A to 3D are assembled;

FIGS. 3A to 3D comprise a second embodiment of the present invention;

FIG. 4 shows selected tracks on the memory drum 31 in FIG. 1;

FIG. 5 is a block diagram showing the assembly of FIGS. 5A and 5B; and

FIGS. 5A and 5B comprise event schedule used to explain the operation of the embodiment illustrated in FIGS. 3A to 3D.

The block diagram (FIG. l)

The number of sorting stations employed in a particular installation is determined by the volume of sorting to be accomplished. Here twenty stations are used and sorting stations i1 and 20 are shown in FIG. l. Each station includes a keyboard 21 for controlling a signal generating mechanism that is generally used in a Teletype- Writer to develop signal patterns in binary code. An operator, by striking selected keys on the keyboard, transcribes the address of each letter into a category code in accordance with an appropriate scheme list of categories.

The scheme list, in one example, may comprise two hundred direct and secondary categories. A direct category is one that requires no further sorting en route or at the post oce of origin, while a secondary category requires further sorting. In this example, the list includes twenty secondary categories, sixteen representing states and four representing groups of states, one hundred and seventy-five direct categories, and five spares.

Each secondary category is encoded in binary in a fourposition code by means of two characters and a command symbol, represented by an asterisk. New York State, for example, is designated by NY. (Note that the second position of the code is blank.) Each direct category is encoded in binary in a four-position code by the characters representing a related secondary category and another prefix. Rochester, N.Y. is therefore designated at RNY. (Note that here the first position of the code is blank.) The number of direct categories assigned to each secondary is determined by the statistical probability of the former.

After observing the address of a letter, an operator generates the related category code by striking the appropriate keys on keyboard 21. When the address is in a direct category, the operator strikes the three characters of the category code, but when the address is a secondary category. the operator strikes the space bar and the two characters of the code. The command code is pre-recorded in the scheme list categories track in memory drum 31 and is provided in control computer 29, when required, as indicated in the above patent application.

After the category code is struck, the letter-handling mechanism is activated and the letter is dropped into a pocket of a shuttle, not shown. The shuttle traverses a rack 27 of sorting slots 24a and deposits the letter in the first vacant slot encountered. When the last-mentioned operation is performed, a code representing the number of the slot into which the letter was deposited is generated.

The letter category code and slot number code are applied to loading butfer units 28 in control computer 29 and are read into the information buffer section 30 of memory drum 31. The codes are then transferred `from section 30 through transfer unit 33 to information analog section 34.

The data stored in section 34 is considered to be information analog, since the slot number and related letter category code are positioned, side-by-side, in successive sectors of memory drum 31 in the same sequence as the corresponding letters stored in slots 24a. It is understood, however, that the codes need not be written on the drum side-by-side so long as each letter category code is provided with a fixed displacement relative to its related number code and the number codes are read out of the memory drum in the same sequence as the slots 24a are positioned in rack Z7.

Each category code in the scheme list is pre-recorded in certain tracks in the tally store section 37. A threshold code, representing the minimum number of letters required for each category before it is selected for unloading, is also recorded in a track in this section. The tally acc-ounting unit 38 keeps a running tally of the number of letters in each category stored in each slot 24a, as indicated by the recordings in analog section 34, and writes this tally in a track in section 37. All the information used to provide self-optimizing inventory reduction is now present in memory drum 3l.

In the operations performed in obtaining optimum inventory reduction, the predominant categories are selected on an alternate basis with a programed category, i.e., the categories in the scheme list are unloaded in turn on an alternate basis with the categories having the greatest number of letters in slots 24a when an active unload category is selected. Accordingly, during certain revolutions of memory drum 31, unload category selector 40 performs one of the following operations:

(a) The predominant category, either direct or secondary, is determined and becomes the next active unload category. (Instead of selecting an active unload category code purely by predominance, the selection may be further constrained by a threshold, so that the category code selected is related to a tally code of desired magnitude.)

(b) The magnitude of a tally of a programed, direct category is compared with the magnitude of its recorded threshold. At the same time, the predominant category is determined. If the tally exceeds its threshold, the direct category is selected. If not, the direct category is skipped and the predominant category becomes the next active unload category.

(c) A search is made for the predominant category. Concurrently, a determination is made of the sum of the tallies of a programed, secondary category and all its associated direct categories, which includes those skipped. lf the magnitude of the sum exceeds the magnitude of the threshold recorded for the secondary category, the letters in the secondary and related direct categories are unloaded together. If the tally fails to exceed its threshold, the predominant category is selected.

After selector 40 has determined the next category of letters to be unloaded from slots 24a, the code representing this category is written on a track in information analog section 34. Each such stack category code written on this track is compared in stack-forming synchronizer 43 with each letter category code in the analog section positioned adjacent the number code of the slot containing the letter. When an identity is found, the number code, related to the letter category code, is read out and passed in binary form, as one output of the stack-forming synchronizer, to decoding matrix 44. The matrix converts the binary code to a pulse on a line connected to one of the slot-gate actuators 45. The energized actuator opens the gate 24h of the related slot to drop the letter on the stack 46 forming on conveyor belt 41.

To optimize inventory reduction, the stack-forming synchronizer 43 makes no exceptions for unloading the letters in slots 24a. The synchronizer therefore instructs tally accounting unit 38 to discount any letter in an active unload category that is added to a slot in advance of the related stack being formed on conveyor belt 41. Thus, the letters that are dropped in slots positioned in advance of the stack will not affect the tally, which is used simply for the selection of the next active unload category.

Another output of synchronizer 43 includes a count of the letters in each stack formed on conveyor belt 41. The count could be used, for example, on the label supplied to the next process machine. Still another output provides an indication of the end of each stack, which could be used in the following process machines to inform a labeller, bundler and poucher as to the location of each stack on conveyor belt 41.

The driving mechanism 50 comprises a synchronous motor for memory drum 31 and a separate synchronous motor for conveyor belt 41. The motors are driven from the same source, and in one embodiment of the present stack-forming synchronizer, the motor for the belt is provided with a gear reduction arrangement, so that the time required for a reference point on the belt to traverse the width of one slot 24a, plus a fixed time interval, is substantially equal to the time required for one revolution of memory drum 31. In another embodiment, the requisite time for the'reference point to traverse the width of one slot is nominally equal to the requisite time for one revolution of the memory drum 31.

The bits engraved in clock tracks 53 to 56 are used to control the timing signal generators 52, which provide the timing signals for control computer 29, as explained in detail in the above patent application. There are twenty-four hundred bits engraved in track 53, and there are forty equally spaced engraved bits on track 54, dividing memory drum 31 into forty equal sectors, each sixty bits long. The start of each sector is aligned with one of the bits engraved on track 53. Track 54 is sensed by a read amplifier whose output is used to provide the 40K pulses and whose output is also used to generate the time gates 40C. Track 56 forms a tach clock containing one prerecorded bit or fiducial mark Y, not shown, which is aligned with a bit in each of the tracks 53 to 55. This track is sensed by a read amplifier to provide an R-bit pulse during each revolution of memory drum 31.

Stack-forming synchronized/first embodiment (FIG. 2)

Brieliy, the function of the stack-forming synchronizer 43 is to control the formation of the stacks of letters on conveyor beit 41. In performing this function, the synchronizer is responsive to ten to thirty active unload category codes selected in the manner set forth in the above patent application.

After being `selected by the selector 40 in FIG. l, an active unload category is transferred through or-gate 439 in FIG. 2 to write amplifier 440. The code is written in serial form in retimer track 441, is sensed by read amplifier 442 and is sent to write amplifier 443. The active unload category code is then written on store track 444 with a one bit advance so that the trail bit of the code is in line with that category code, if any, recorded in tracks 223 for slot 1 of the twenty-four hundred slots 24a. (See FIG. 4).

It will be recalled that a letter category code and slot number code are generated for each letter deposited in a slot 24a. These codes are transferred from the information buffer section 30 (FIG. 1) through the transfer unit 33 to the information analog section 34. Tracks 223 and 204 (FIG. 2) are located in the analog section. Hence, as explained in the above-identified appiication, the slot number code, generated when a letter is deposited in one of the slots 24a, is used in such a manner that the related letter category code will be passed through orgates 221 to write amplifiers 222 and will be recorded in a position on tracks 223 adjacent the slot number code prerecorded on tracks 204, that is identical to the generated number code. (See FIG. 4). Hence, each number and related category code are positioned, side-by-side, in successive sectors of memory drum 31 in the same sequence and proportioanl location as the corresponding letters stored in slots 24a.

It is noted here that the twenty-four hundred bits of tracks 204 are divided into forty sectors, each sixty bits long. Two of these sectors are assigned to each station 1 to 20, and each sector contains in parallel form the slot numbers, one to sixty, of half the slots of a rack 27. One of the 40" sectors is shown in FIG. 4.

A reference point on conveyor belt 41 represents the trailing edge of the space allocated to the formation of a stack 46 on the belt. It will be recalled that the time required for a point on the belt to traverse the width of one slot 24a, plus a fixed interval of time, is equal to the time required for one revolution of memory drum 31. Accordingly, an active unload category code is written on track 441 when the reference point passes a nominal O-slot and is read for the first time by read amplifier 447 when the reference point, minus one twentyfour hundredth of the space allocated to the formation of a stack, approaches the l-slot of slots 24a.

The active unload category code on track 444 is read continuously into -bit shift register 448 by means of read amplifier 447. With no more than thirty twenty-bit letter category codes, regularly spaced on this twenty-four hundred bit track, the blank gaps between the category codes is invariably more than twenty bits. Because it is not possible for the beginning and end of successive codes to be in register 448 at once, it is possible to indicate that a complete code is contained in the register by applying the lead and trail bits to and-gate 449. An output from this and-gate indicates that a complete category code is present in the register.

Assume that a direct, active unload category is read out of track 444 for the first time and is recorded in register 44S. Simultaneously, read amplifiers 237 read the category code in tracks 223 that is releated to slot 1 of slots 24a. Character No. 1 in the output of the read amplifiers and in register 443 are compared in comparator 458, while character Nos. 2 and 3 are compared in comparator 459. When identities are found, the output of comparator 453 is applied to and-gate 460 and the output of comparator 459 is branched to and-gates 460, 463. Since a l bit is located at both ends of register 448, theoutput of and-gate 449 enables and-gate 460 to pass a signal through or-gate 464 to 465, which represents six and-gates. The code number of slot 1 is now read from tracks 204 by read amplifiers 466 and is passed, in parallel form, through and-gates 465 to the decoding matrix 44. The matrix ,is then controlled, in a manner described in detail in the above patent application, to effect the discharge of the letter in slot 1 to the conveyor belt 41 in FIG. l, thereby starting the formation of a stack of letters on the conveyor belt.

Summarizing the above operations, the active unload category code is read out of store track 444 and is positioned in register 448. The related category code is read out of tracks 223 and is compared in comparators 458, 459 with the unload category code. Since an identity is found in each comparator, the slot number in tracks 204, on line with the category code, is applied to the decoding matrix 44, which generates a gate-release signal. The latter signal is applied to the pertinent one of the slot-gate actuators 45 in FIG. l, so that the letter contained in the associated slot 24a is discharged to start the formation of a stack 46 on conveyor belt 41.

Returning to FIG. 2, and-gate 478 and inverter 479 form and-not-gate 480. In the absence of an R-bit pulse on inverter 479 and the presence of a 40K pulse on andgate 478, the latter and-gate provides an output signal that is applied to terminal 1 of fiip-flop 481, turning the latter an. The flip-flop remains on until turned off in the manner described below.

The output of fiip-tiop 481 enables and-gate 486 and the active unload category code under consideration passes bit-by-bit through register 448, the latter and-gate and or-gate 439 to write amplifier 440. The code is then written on track 441, sensed by read amplifier 442 and advanced one bit on track 444 from the position in which `it was previously written on this track. The trail bit of the active unload category code is now .in line with the letter category code, if any, recorded in tracks 223 and the number code, recorded in tracks 204 for the letter in slot 2 of slots 24a.

It should be noted that after a category code is read and before the code is rewritten on either track 441 or 444, the category code is erased by an erase head not shown in FIG. 2.

The operations, described in detail above, are now repeated with the category code written in tracks 223 for slot 2 of slots 24a. If identities are obtained in comparators 453 and 459 or in comparators 459 and 489, as in dicated below, the slot number code, read from tracks 204, is transmitted to decoding matrix 44 to permit the letter in slot 2 to be discharged into the stack 46 forming on conveyor belt 41 in FIG. 1. The same sequence of operations are performed for the remaining slots 24a.

The conveyor belt advances the Width of one slot 24a minus a small, fixed distance for each revolution of memory drum 31, so that each letter added to a stack 46 in FIG. l drops to a location on the belt slightly in advance of the previous letter. Ideally, each letter of a stack will partially overlap the previous letter so as to present an orderly feathered arrangement.

The example presented in detail above relates to a direct category code. When a secondary category code, say NY, is selected through predominance as an active unload category code, only the characters NY are written on track 444. When this category code is read out of track 444 and is shifted through register 448, character No. 1 in the register is blank and characters Nos. 2 and 3 are N and Y, respectively. If #NY is Written in tracks 223 on line with this active unload category code, identities are found in comparators 458, 459. As set forth in the example above, the outputs of these comparators enable `and gates 465 to pass the slot number, read out of tracks 204, to the decoding matrix 44. This will effect the discharge of the letter in the related slot 24 to the appropriate stack 46 forming on the conveyor belt 41.

In contrast, when the secondary category code is sclected as an active unload category code through a programed opportunity, the characters *NY are written on track 444 and the command code and characters N and Y are then recorded in register 448. Since the command code in the register is compared in comparator 489 with the command code provided by the 6-bit command reference source 490, each time that a letter category code ending in NY is encountered on tracks 223 in line with this active unload category code, the associated letter in one of the slots 24a is discharged to the stack 46 forming on conveyor belt 41. Thus, the stack comprises letters in the secondary code NY and in the direct categories associated with the same. It should he noted here that the output of command reference source 490 and the command code in register 448, when applied to comparator 489, permits ignoring character No. 1 of the asso` ciated direct category codes written on tracks 223.

In view of the foregoing, it will be apparent that each time one of the active unload categories is read out of track 444, it is returned to that track with a one bit advance in angular position. In effect, the read amplifier 447 senses each active unload category during one revolution of memory drum 31 and on the succeeding revolution each code is advanced into alignment with the category code and slot number code for the next slot 24a. Hence, starting at slot 1 each active unload category code traverses track 444 and is sequentially compared with a letter category code for each slot 24a. When identities are found in either comparators 458 and 459 or compara` tors 459 and 489, a signal is generated and applied to decoding matrix 44 to control the formation of a stack of letters, associated with that unload category, on co-nveyor belt 41.

In keeping a running inventory of the categories of the letters in slots 24a, a letter is not counted if it is in an active unload category and is positioned in a slot in advance of the stack 46 forming on conveyor belt 41 for this category` The arrangement for accomplishing this result is in the tally accounting unit 33 (FIG. l) and is responsive to character Nos. 1 to 3 in register 448 or the output of comparator 489 and characters Nos. 2 and 3 in the register. For further details of this arrangement, reference is made to the above-identified patent application.

The arrangement for erasing the letter category codes from track 223 will now be discussed. When a letter category code is written on tracks 223 in line with an identical direct unload category code, identities are obtained in comparators 458, 459. The output of and-gate 460 is then directed through or-gate 464 to write amplifier 471, is written on retimer track 472, sensed by read arnplitier 475 and converted to an erase signal by eraser 476. The output of 476 is passed through or-gate 221 to the eighteen write amplifiers 222, erasing that category code which had produced the identity signal when read out of these tracks by read ampliers 237 and applied to the comparators.

When a category code is written on tracks 223 in line with an identical secondary active unload category code, derived through predominance, identities are obtained in comparators 458, 459 and the code on tracks 223 is erased in the manner just indicated. Finally, when relevant category code on tracks 223 is in line with the secondary active unload category code, derived through a programed opportunity, identities are found in comparators 4519, 489

and the category code on tracks 223 is erased, again in the manner indicated above. Here, it should be noted that the associated direct category codes on tracks 223 are included for erasure.

The output of and-gate 449 coincides with the R-bit pulse in and-gate 477 only upon the full circumferential traverse of track 444 by an active unload category code. At this time, a signal is applied to terminal 0 of liip-op 481, turning the latter ot, so that the information in register 448 will not pass through and-gate 486 to write ampliher 440, but will pass through and-gate 483, enabled by the inverter 485, in and-not-gate 484 to the next machine. The next 40K pulse passes through and-gate 478 to terminal 1 of flip-flop 481, turning the latter on. The output of the tiip-op is then applied to inverter 485, andgate 483 is inhibited, While and-gate 486 is enabled to pass the next information in register 448 to Write amplifier 440. Thus, a time gate, sixty bits long, is provided during which the output of register 448 is directed to the next process machine instead of to write amplifier 440.

As described in detail in the above patent application, each sorting station 1 to 20 contains a rack divided into rack-half X and rack-half Y. Since there are sixty slots 24a in each rack-half, there are, in total, twenty-four hundred slots. Each slot is provided with a normally-closed discharge gate 24h (FIG. 1) that is adapted to `be opened by a release mechanism described in detail in U.S. Patent No. 2,863,574. The release mechanism for each gate is controlled by a solenoid connected to a respective one of twenty-four hundred lines in the output of decoding matrix 44. The release mechanisms and solenoids for all the gates 24h are designated by the slot-gate actuators 45 in FIG. l.

Each slot number code in tracks 204, when related to an active unload category, is passed through and-gates 465, in parallel form, to decoding matrix 44. Time gates 40C comprise forty components, generated in sequence. The active time gates applied to decoding matrix 44 together with the six bits of the number code cause a slot unload signal to be applied to one of the lines in the output of the matrix. Thus, when the code of a slot number is applied to the matrix, a signal appears on one of its twenty-four hundred output lines to energize a solenoid which operates a release mechanism to open a discharge gate 24b. A letter is then discharged by gravity from the associated slot 24a to conveyor belt 41 (FIG. 1). Subsequent deenergization of the solenoid operates a reset mechanism, described in U.S. Patent No. 2,863,574, to cause the discharge gate to close.

Stack-forming synchronizer, second embodiment (FIGS. 3A t0 3D) With reference to FIG. 3B, tracks 223 and 204 are located in the analog section 34 in FIG. l.

As previously explained, a slot number code is generated whenever a letter is deposited in one of the slots 24a. This code is used to control the routing of a related letter category code, which is passed through or-gate 221 to write amplifiers 222 and is then written on tracks 223 efficaciously adjacent to a number code that is prerecorded in tracks 204. The prerecorded code is identical to the generated number code. (See FIG. 4.) Thus, each number and related category code are positioned side-by-side on drum 31 in the same sequence as the corresponding letters stored in slots 24a.

As will be described later, flip-flop 169 (FIG. 3D) is normally on, being turned otf only for a time interval of sixty ,bits duration after an active unload category code has traversed track 444. (See Fiducial Record, infra.) Hence, the hip-flop applies a signal to and-gate 262 which is normally enabled to pass the contents of register 138. On the other hand, flip-flop 167 (FlG. 3D) is normally turned off unless identities are found in the second comparing-position of register 11318. Hence,

and-gate 251 is normally blocked from passing the contents of register 138.

With reference to FIG. 3A, the next active unload category code, received from selector 40 in FIG. l, is passed through or-gate 12S, 2l-b1`t register 138, normally enabled and-gate 2612, write amplifier 126 and is recorded on retimer track 127. The category code is sensed by read amplifier 130 and is sent through orgate 131 to write amplifier 132. The code is then recorded on store track 444 with a one bit advance, is sensed by read amplifier 134, passed through or-gate 125 and is re-registered in 138.

As `will be set forth in detail below, a fiducial record, indicating the zero letter position of a stack 46, is kept on store track 279. To keep this record, the next active unload category code is passed through or-gate 280 to the -bit register 300 (FIG. 3A). The code is shifted through the register bit-by-bit, is passed through normally enabled and-gate 305 to write amplifier 2811. The code is then written on retimer track 282, sensed by read amplifier 283 and is written `by write amplifier 284 on track 279 with a one bit advance. This active unload category code, sometimes referred to hereinafter as the duplicate unload category code, is read by read amplifier 286 and is passed through or-gate 280` to register 300.

Here it is noted that track 279 contains 2400 bit places, each aligned with a bit place in track 444.

The spacing of stacks of lette-rs 46 on conveyor belt 41 (FIG. l), and thus the spacing between active unload category codes, is adjusted by means of Rev. SS device 102 in FIG. 3 of the above-mentioned patent application` This spacing is adjusted so that when the next active unload category code is passed through orgates 125 or 280 to register 138 or 300, respectively, there will rbe no interference between this code and one read out of track 444 or 279. (It will be apparent that if the active unload category codes do not interfere in registers `138 and 300, they will not interfere when written on tracks 444 and 279).

To avoid interference, registers 138 and 300 must be cleared of information for an interval of time between the recording of each category code therein. This is accomplished primarily by setting the pitch of stacks 46 by means of device 102 at a value greater than twice the bit length of the longest register, in this case, 138.

However, this expedient does not take into account the need for a space on tracks 444 and 279 that is unoccupied at the time that the next active unload category code is recorded in registers `138 ,and 300. If this space on either track were occupied, the code recorded therein after being read out, would interfere with the code being recorded in the `associated register. Thus, at the time that the trail bit of the next active unload category code passes through or-gate 125, the lead bit of the next code to be read out of track 444 must be at least twenty bits from the latter or-gate. A corresponding unoccupied space must be provided on track 279.

When the Oabit and the 2400-bit position coincide on memory drum 31, as in the present embodiment, the unoccupied space on tracks 444 and 279 may be obtained by the proper selection of the stack pitch. More specifically, a pitch may be chosen by trial and error such that when divided into the total number of bit positions in a track on drum 31, a whole number is not obtained, but a number is obtained with a remainder which represents the unoccupied space on the tracks required for recording the next active unload category code in registers 138 and 300 without interference. (The last space on tracks 444 and 279, occupied by the oldest category code before passing to the next process machine, is the same as that first occupied by the next active unload category code.)

As an example, using as a practical number of forming stacks on conveyor belt 41, the stack pitch, disregarding interference, would be 2400/30 or 80. To

obtain a remainder, the pitch is selected to be 78 so that 2400 divided by 78 equals 30 stacks forming, plus 60 bit-places left over to avoid interference. Subtracting 42 (twice the bit-places of register 138) from 60 leaves IS-bitaplaces, which allows for a count of 36 letters, per stack. To enable a larger letter count, the number of forming stacks may be adjusted downward.

It is obvious that a set of operative stack or active unload category code pitches may be predetermined for a fully specitied machine.

In another arrangement to avoid interference, memory drum 31 may be dimensioned so that the O-slot and 2400-slot positions do not coincide. The positions may be separated by an otherwise unused part of the drum, representing unused or nonexistent slots 24a.

It will be recalled that active unload category code comprises eighteen category information bits which are preceded by a lead bit and followed by a trail bit. When the trail and lead bits are in the first and twentieth places, respectively, of register 138, the trail bit is in line with a number code in tracks 204 and with a letter category code in tracks 223. (See FIG. 4). This particular alignment of the trail bit is referred to hereinafter as the read point V.

The next active unload category code, received from selector 40 in FIG. 1, is initially branched to and-gate 143 (FIG. 3C) and to l9-bit delay device 144. The output of 144 enables and-gate 143 to pass a single bit through or-gate 147, l-bit delay device 210 and normally enabled and-gates 209 and 211 to write amplitier 148. The bit is then recorded on retimer track `149, sensed by read amplifier and sent through or-gate 15.1 to write amplifier 152. The bit is recorded on store track with a one bit advance in line with the above trail bit (see FIG. 4) and is referred to hereinafter as the odd-even mark O. The read point and odd-even mark are discussed in greater detail in connection with the event schedule in FIGS. 5A, 5B.

Since it is desired that the initial reading of the oddeven mark O and the trail bits of the active unload category codes be obtained simultaneously on read amplifiers 156, 134 and 286, the information is entered intially into delay device 210, and or-gates 125, 280.

It will be apparent that there are several information advancing circuits in FIGS. 3A and 3B, that are exemplified by one that comprises retimer track 253, store track 444, the related read and write amplifiers and register 138. These circuits are characterized by a mode of operation wherein the information is read out of the store track, is written on the retimer track and repositioned on the store track with a predetermined advance from the position where it was last read out.

Now consider the initial synchronizing requirements relative to the several information advancing circuits. The position of the heads of the read and write amplifiers of the various retimer tracks are adjusted to reposition the information as well as to compensate for the delays introduced in the circuits. Hence, because of the delay introduced by register 138, retimer tracks 127 and 253 are compensated twenty bits besides the adjustments for their respective one and two bit advances.

In general, considering the bit pulse as a measure of time and one revolution of drum 31 as requiring 2400 bit pulses, a unit of coded information on a store track may be repositioned one bit by providing a retimer track and read, write and erasing means positioned so that the sum of the codes traverse of the advancing circuit is 2399 or 2401 bit pulses; the latter alternatives govern the direction of the traverse of the code on the store track relative to the rotation of memory drum 31. As a more specific example, assume the direction of rotation of drum 31 is such that the bit places of store track 444, starting with the 1-bit place, pass in sequence under the read head of amplifier 134. Assume further that the trail bit of an active unload category is recorded in the 2-bit place of 1 1 store track 444. Then, if the sum of the traverse of the advancing circuit is 2399 bit pulses, the trail bit will be rewritten in the l-bit place of the track, while if the sum of traverse of the advancing circuit is 2401, the bit will be rewritten in the 3-bit place.

In this connection, it should be noted that each of the retimer tracks 282, 127, 253, 149, and 271 are provided with conventional erasing means, not shown, positioned after the heads of their read amplifiers and immediately before the heads of their write amplifiers, so that the information recorded on each track is erased after being read out.

The odd-even mark O indicates the count status of a stack of letters 46, and the control logic, described below, uses this indication of status. An even count is indicated by coincidence of the odd-even mark with the output of and-gate 161 (FIG. 3A). Thus, an even-stack count is indicated by the output signal of and-gate 160 (FIG. 3C). When an output of and-gate 161 occurs without an oddeven mark reinforcement, it is understood that the count of the stack is odd.

At the start of an example of operation to be considered now, there are no letters in a stack 46, and the related odd-even mark O and read point V are in line with the O-slot. (See FIG. 4). Read amplifier 156 (FIG. 3B) reads track 155 and applies the odd-even mark O recorded therein to and-gate 160 (FIG. 3C). Simultaneously, a l bit of an active unload category code is registered in the first and twentieth places of register 138. That is to say, the active unload category code is registered in the first comparingposition of the register, and this enables and-gate 161 to apply a signal to and-gate 160.

The output of and-gate 160 is transmitted to inverter 163, which together with the six and-gates 164 and the twelve and-gates 165 comprise eighteen and-not-gates 166. 5

Since a signal is applied to inverter 163, the code in register 138 can not pass through and-gates 164, 165.

The output of and-gate 160 is branched through oir-gate 170 to terminal 1 of thc odd-count addition flip-op 171, turning the flip-flop on. The output of the or-gate is also branched through 2-bit delay device 172 to terminal O of the liip-op, so that after a two-bit delay the flip-flop is turned off. When activated, the output of the flip-Hop is applied in parallel to 173 and 174, illustrating six and twelve and-gates, respectively.

After the active unload category code in register `138 shifts one place, the trail bit of the code is in the second bit place, eicaciously in line with the next slot number code in tracks 204, and the lead bit is in the twenty-first bit place. The active unload category code is now in the second comparing-position of register 138, and coincidence of the l bits and-gate 178 enables the latter to transmit a signal to and-gates 173, 174. Character No. 1 of the category code in register 138 is now passed in parallel form through and-gates 173 and or-gates 180 to comparators 181 and 182. Likewise, characters Nos. 2 and 3 in register 138 are passed in parallel form through and-gates 174, or-gates 183 to comparator 185.

Assume that the category code read out of track 223 by read amplifiers 175 is a direct category code and is the same as the active unload category code in register 138. Then, identities will be obtained in comparators 182, 185 and the output of these comparators will enable and-gate 186 to send a signal through or-gate 187 to and-gate 188 (FIG. 3D). On coincidence of the outputs of and-gate 178 and or-gate 187 in and-gate 188, the latter transmits a signal to inverter 190 to inhibit the eighteen and-not gates 192. Hence the slot number code, read out of tracks 204 by read amplifiers 176, can not pass through the six and-gates 191 to decoding matrix 44.

The output of or-gate 187 is branched to write amplifier 195 and is written on retimer track 196. This track is sensed by read amplifier 197, which applies its output to eraser 198 to provide an erase signal that is passed through or-gate 221 to write amplifiers 222, thereby erasing the category code that was identified by comparators 182 and 185 in the manner described above.

If the active unload category code in register 138 had been for a program-derived secondary category, the command code in the register would have been compared in comparator 181 with the command code provided by 6- bit command reference source 230. Similarly, character Nos. 2 and 3 in 138 would have been compared in comparator 185 with the characters read from track 223. On the occurrence of identities, the outputs of these comparators would have enabled and-gate 231 to transmit an identity signal through or-gate 187 to and-gate 188. Again, the output of or-gate 187 is branched to write amplifier 195 and written on retimer track 196.

It will be apparent that the cooperation among register 138, comparators 181, 182, 185, source 230 and track 223 in the second embodiment is essentially the same as the cooperation among register 448, comparators 458, 459, 489, source 490 and tracks 223 in the first embodiment (FIG. 2). Accordingly, for other modes of operation of the first group of components just listed, attention is directed to the corresponding components in the first ernbodiment.

The output of comparator 181 and the signals applied through or-gates 180, 183 are transmitted to the tally accounting unit 38 (FIG. 1) and inhibit the advance of a counter contained therein. This is accomplished in the same way as the output of comparator 489 and the inputs to each comparator 458, 459 derived from register 448 in the first embodiment of the stack-forming synchronizer presented above.

The read heads of amplifiers 220, 215, 197 and the write heads of amplifiers 222 are in timing alignment and 180 away from the timing aligned read heads for amplifiers 176, 175, 156 and the write head for amplifier 195. An erase head is positioned, but not shown, near each retimer track 282, 149 and 271 and store track 155 immediately before the write head of each write amplifier associated with the track.

It will be recalled that at the start of the present example the read point and the oddeven mark O were in line with the O-slot. The latter mark was read out of track by read amplifier 156 and was erased just before reaching the write amplifier 152. However, since identities were not found when the active unload category code was in the first comparing-position of register 138, the odd-even mark is re-recorded by means of write amplifier 152 with a one bit advance on track 155 in the fashion described in detail below. The odd-even mark is, in effect, recorded one bit after the read point. Since identities were found when the unload category code was in the second comparing-position of register 138, write amplifier 195 records the output of or-gate 187 on track 196 as a bit, occurring etiicaciously one bit after the read point. Thus, read amplifier 215 reads the odd-even mark O on track 155 at the same time that read amplifier 197 reads the latter bit on track 196, and there is coincidence of the outputs of the amplifiers in and-gate 216. The output of and-gate 216 enables and-gates 217, and a slot number code is read by read amplifiers 220 from tracks 204. This number is the one in line with the letter category code under consideration, since both codes moved the same between readings. The output of read amplifiers 220 is passed through and-gates 217 and stored in parallel form in 6bit register 218.

In the absence of a signal to inverter 226 in and-not gates 227, the output of register 218 is passed through the six and-gates 228, in parallel form, to decoding matrix 44. As set forth in the patent application mentioned above and summarized in connection with the first embodiment, the matrix generates a slot unload signal that is used to release the letter from the slot 24a (FIG. 1) assigned the slot number code just read out of tracks 204. This letter is the first in the stack, is discharged 13 to a half-slot place on conveyor belt 41 and comprises an odd-count addition.

The outputs of and-gates 228 are branched to or-gate 231 which will pass any signal present in register 218 and thereby clear the register.

Normally the output of register 218 is not inhibited by and-gates 228. However, an even count addition may occur for another stack at the same time that a slot number code is contained in register 218, and its identity signal passed through or-gate 187 to and-gate 232. Since a l bit is in the rst and twentieth bit place of register 138, the latter and-gate is enabled by the concurrent output of and-gate 161, to apply a signal of one bit duration to inverter 226. And-gates 228 will then be inhibited for the time interval of a single bit. This inhibition will seldom coincide with the code present in `register 218, since such coincidence requires that identities be found at the exact angular offset of the two sets of aligned heads mentioned above, and on occurrence will produce only a minuscule positioning error of the related letter on its stack 46.

From the example just considered, it is apparent that when an active unload category code is in the first comparing-position in register 138 and an odd-even mark O and read point V are in line, the letter-category code for the next slot 24a is compared with an active unload category code in the second comparing-position in the register. When identities are found in the second comparing-position, a letter, comprising an odd-count addition, is released from a slot 24a after memory drum 31 has made one-half revolution from the point at which the identities were found. The letter occupies a half-slot place in a related stack 46.

As another example of operation, assume that stack 46 has an odd-count, the read point V and the odd-even mark O are not in line, and the active unload category code is in the rst comparing-position in register 138. Since the read point and odd-even mark are not in line, and-gate 160 is blocked and `the output of and-gate 161 can not pass through the former and-gate to inverter 163. Thus, character No. 1 in the register will pass through and-gates 164 and or-gates 180 to comparators 181 and 182, and character Nos. 2 and 3 will pass through andgates 165 and or-gates 183 to comparator 185.

Assume further that the slot on line with the read point V contains a letter in the category designated by the active unload category code. Identities will be obtained in comparators 181 and 185 or 182 and 185, and a signal will be applied through or-gate 187 to and-gates 191. The latter will then pass the slot number code, read out of tracks 204, to the decoding matrix 44. A letter will be released from the slot, associated with the latter code, to form an even-count addition, so that the count of the stack is now even.

When the output of and-gate 161 and the output of orgate 187 coincide in and-gate 232, the latter transmits a signal through or-gate 170 to terminal 1 of ip-op 171. Thus, flip-flop 171 may be set either by the finding of an even-count addition to an odd-count stack, as just indicated, or by `the output of and-gate 160, representing an even stack count.

After the active unload category code is shifted one bit place to the second comparing-position in register 138 and Hip-flop 171 is turned on, character No. 1 in the register is passed through and-gates 173 to comparators 181 and 182, while character Nos. 2 and 3 are passed through and-gates 174 to comparator 185. The letter category code for the next slot 24a, i.e., the one following the slot just checked, is read out of tracks 223 and applied to the comparators. If identities are found, the operation becomes the same as the first example above, and the letter in the associated slot is released to the stack, forming an odd-count addition. The count of the stack is now odd.

If identities had not been found in the first comparingposition in register 138, the lack of output of or-gate 187 would not have enabled and-gate 232 to turn on tliptiop 171. Consequently, a comparison could not have been made between the unload category code in the second comparing-position and the letter category code, if any, for the next slot 24a, read out of tracks 223.

From the last example, it is seen that when an active unload category code is in the first comparing-position in register 138 at a time when this read point V is not in line with the odd-even mark O, and the letter category code for the related slot is the same as the active unload category code then, and only then, will the letter category code for the following slot be checked at the next bit pulse, rather than after the next revolution of memory drum 3l.

To summarize the description presented so far: each active unload category code is read, in turn, out of store track 444 and is moved bit-by-bit through register 138, where the code may be compared at a first and then at a second comparing-position with first one letter category code and then another read out of tracks 223. During the first comparison, the tirst place of 138 contains the codes trail bit at the same time that a slot number code on tracks 204 is sensed by read amplifiers 176. During the second comparison, one bit later, after the code has shifted one place in register 138, the next advanced slot number code in tracks 204 is sensed. The number and category codes sensed when the unload category code is in the first comparing-position are related to a particular one of the slots 24a. The codes sensed when the unload code is in the second comparing-position are related to the next advanced slot 24a.

Accordingly, during one revolution of memory drum 31, each active unload category code, written on track 444, may be compared separately with the letter category code of first one slot 24a and then the next advanced slot. These two comparisons are separated by a time delay of one bit pulse.

If the two slots were unloaded on the occurrence of their related comparisons, practically simultaneously, the two letters would -be separated on conveyor belt 41 `by substantially a whole slot place. For this reason, only the rst comparison is permitted to produce a slot unload signal in decoding matrix 44 at the point of comparison. When identities are found during the second comparison, the slot unload signal is produced after a delay of half-arevolution of memory drum 31, when conveyor belt 41 has moved halte-slot space toward the slot 24a containingr the pertinent letter. Thus, the even-count additions fill the whole-slot places and the odd-count additions fill the half-slot places in a stack 46.

Because each letter is dropped to build on the leading edge of a stack as it forms on conveyor belt 41, the active unload category code must be properly advanced on track 444 to pace the buildup. Hence when an oddcount addition is made to a stack, the code is advanced two bit places on track 444. This means that when the stack has an odd count, the code is, in effect, recorded on track 444 at half-a-slot advance from the leading edge of the stack.

When an even-count addition is made to a stack, the active unload category code on track 444 is advanced the regular one bit place to match the constant advance on conveyor belt 41. Thus, when the stack has an even count, the codes eflicacionsly recorded on track 444 in line with the leading edge of the stack.

When an addition is not made to a stack 46, because identities are not found in the first and second comparingposition in register 138, the active unload category code is advanced one bit place on track 444.

An odd-even count record is kept on store track by an odd-even mark O associated with the active unload category code for a stack 46. This mark records an even count when in line with its unload category code and records an odd count when it is one bit place behind its 15 unload category code. For this record, when an evencount addition is made to a stack 46, the odd-even mark O is advanced two bits during the following revolution of memory drum 31; otherwise, the mark is advanced one bit place on track 155 for each revolution.

The arrangement for achieving these operations will be described in detail just below.

Assume that a stack 46 has an even count and that an active unload category code is recorded in the second comparing-position of register 138. Assume further that flip-flop 169 is turned on, iiipdiop 167 is turned off, and identities are found either in comparators 181 or 182 and comparator 185, so that an odd-count addition is made to the stack.

Then, flip-flop 169 applies a signal to and-gate 251. The output of or-gate 187 and the output of and-gate 178 enable and-gate 188 to send a signal to terminal 1 of flip-Hop 167, turning the latter on. The output of flip-liep 167 is branched to inverter 260 in and-not gate 261, thereby inhibiting the and-not gate. The output of flip-Hop 167 is also branched to and-gate 251, which is then enabled to pass the active category code in register 138 to write amplifier 252. The code is written on retimer track 253, sensed by read amplier 254 and passed through or-gate 131 to write amplifier 132. The code is then recorded on store track 444 with a two bit advance.

Thus, it is seen that when identities are found in the second comparing-position of register 138 an odd-count addition is made to stack 46, and the active unload category code is advanced two bit places on track 444 during the revolution of memory drum 31 that occurs after the comparison. Since the unload category code is advanced two bit places, the read point V is advanced the equivalent of two bit places.

Assume that a stack 46 has an odd count and that an active unload category code is recorded in the first comparing-position of register 138. And-gate 161 will then apply a signal to terminal of flip-flop 167, turning the latter off. And-gate 251 is blocked, while and-gate 262 is enabled. Assume further that flip-flop 169 is turned on, and identities are found in either comparators 181 or 182 and comparator 185. Under these conditions, an even-count addition is made to the stack 46.

The active unload category code is then shifted one bit position to the second comparingposition of register 138 where a comparison is permitted (by action of ipflop 171, as described earlier) and where, it is assumed further, no identity is found. The unload category code is then shifted bit-by-bit through the remainder of register 138 and through and-gate 262 to write amplifier 126. The code is recorded on retimer track 127, is sensed by read amplifier 130 and is re-recorded on store track 444 with a one bit advance.

Hence, when identities are found in the rst comparingposition of register 138, an even-count addition is made to a stack 46. and the active unload category code is advanced one bit place on track 444 during the revolution of memory drum 31 that occurs after the comparison. Since the latter point is advanced one bit place, the read point V is likewise advanced the equivalent of one bit place. (This example assumes, of course, that identities will not be found in the second comparing-position in register 138. lf the latter occurs, the unload category code is advanced two bit places on track 444, as set forth above.)

In addition when identities are not found in either the first or second comparing-positions of register 138, flipop 167 is not turned on, and-gate 251 is blocked, but and-gate 262 is enabled to pass the active unload category code. The code is then re-recorded on track 444 with a one bit advance.

With reference to the odd-even mark, consider the following example. The active unload category code is recorded in the first comparing-position of register 138.

The odd-even mark and the read point V are not in line, so that the output signal of and-gate 161 does not coincide with the odd-even mark in and-gate 160, indicating that the count of the related stack 46 is odd. Identities are found in comparators 181 and 18S or 182 and 185, so that an even-count addition is made to the stack. Under these conditions, the read point V (signaled from and-gate 161) and the output of or-gate 187 coincide in and-gate 232. The output of the latter and-gate is applied to inverter 213, blocking and-gate 211. The output is also applied t0 and-gate 268 to enable the latter to pass the odd-even mark to write amplifier 269. The mark is then written on track 271, is sensed by read amplier 272, passed through or-gate 151 and is rewritten or store track 155 with a two bit advance.

Thus when the odd-even mark O and read point V are not in line, an odd count of the related stack 46 is indicated, and when identities are found in the rst comparing-position of register 138, the odd-even mark is advanced two bit places on store track 155 during the following revolution of memory drum 31.

It will be apparent that when the odd-even mark and the read point are not in line and identities are not found in the first comparing-position of register 138, the oddeven mark, read out of track 155, will pass through andgate 211, instead of 268, and will be advanced one bit pla-ce on track 155 during the following revolution of memory drum 31. Likewise, when the read point V and odd-even mark O are in line (denoting an even count of stack 46), the output of and-gate 160 will block andgates 164, 165, so that no identities can be found in comparators 181, 182 and 185, and the odd-even mark will be advanced one bit place on track 155 during the next revolution of memory drum 31.

At this point, it is of interest to consider the function of delay device 210. With reference to FIGS. 5A and 5B, it is noted that the tracks of drum 31 traverse any stationary point, such as a read head, from right to left and that the odd-even mark O is either in line with or one slot to the left of the read point V. In the latter case, the odd-even mark will be read out of track 155 one bit ahead of the point at which the trail bit of the unload category code relative to read point V is read out of track 444. When the two marks are not in line and identities are found in comparators 181 or 182 and 185, it is desired that the output of and-gate 232 and the odd-even mark coincide in and-gate 268 to permit the odd-even mark to advance two bit places, as described above. To achieve this result, the delay device 210 provides the odd-even mark with the necessary one bit delay.

In summary, when the stack count is even and an identity is found with the active unload category code in the second comparing-position in register 138, the oddeven mark O is advanced one bit place on store track 155. When the stack count is odd and identities are not found with the active unload category code in either the first or second comparing-position in register 138, the odd-even mark O is advanced one bit place on track 155. Furthermore, only when the stack count is odd and an even-count addition is found at its only designated opportunity, read point V, then and only then, is the oddeven mark O provided with a two bit advance.

Fiducia] record (FIGS. 3A and 3D) A fiducial record, that indicates the zero letter position of a stack 46, is kept on store track 279 and is passed to subsequent stack-processing stations.

As set forth earlier, a duplicate of each active unload category code is entered on track 279 at the time that the code is entered on store track 444. During each revolution of drum 31, the duplicate code is read out of track 279, shifted through register 300 and through andgate 305 to write amplifier 281. The code is written on track 282, sensed by read amplifier 283 and is rewritten on track 279 with a one bit advance.

It will be recalled that the time required for a reference point on conveyor belt 41 to traverse one slot 24a is essentially equal to the time required for one revolution of memory drum 31. Since there are twenty-four hundred slots and the same number of bit places on track 279, one bit advance per revolution provides the duplicate code with a uniform traverse of track 279. This represents a uniform traverse of slots 24a by a reference point on conveyor belt 41.

At the end of traverse of track 444 by an unload category code, the l bits, recorded in the rst and twentieth places of register 138, enable and-gate 161, whose output coincides with an R-pulse in and-gate 168 (FIG. 3D). The output of the latter and-gate then turns off ioop 169 to block and-gates 251 and 262. The ip-op is turned on by the next 40K pulse, passing through and-gate 202. In this way, `and-gates 251, 262 are blocked for a period of sixty bits long, which is adequate to prevent the code in register 138 from being re-recorded on tracks 253 or 127.

At the end of traverse of track 279 by the duplicate code, the 1" bits, recorded in the first and twentieth places of register 300, coincide with the last-mentioned R-pulse in Vand-gate 301, which is enabled to turn on ipflop 302. The output of the flip-Hop is applied to inverter 303 in and-not gate 304 to block and-gate 30S, so that the duplicate code can not be rewritten on track 282. At the same time, the output of 300 is branched to andgate 285, permitting transfer of the duplicate code, whose trail bit is the fiducial mark, to the next process station.

Count of letters in a stack (FIGS. 3A and 3D) As previously described, an active unload category code and its duplicate are recorded simultaneously on tracks 444 and 279, respectively. The duplicate represents the zero letter position of a related stack on conveyor belt 41.

The letters in an unload category are discharged from slots 24a to the belt at successive half-slot places, advancing head of the zero letter position in a stack. To pace the build-up of letters, during each revolution of memory drum 31, the unload category code is advanced either one or two bit places on track 444. The duplicate code, however, is advanced only one bit place on track 279 per revolution, and remains at the zero letter position. Accordingly, the trail bit of the unload category code on track 444, within half-a-slot, indicates the leading edge of a stack 46, while the trail bit of the duplicate code on track 279 indicates the zero letter position of the stack.

Since a letter is dropped in each whole slot and halfslot place, the count of the letters in a stack is equal to twice the number of bit places that separate the trail bit of the code on track 444 and the trail bit of the related code on 279, plus nothing for an even-count stack, or minus one for an odd-count stack. The number of letters in a stack 46 may, therefore, be obtained by counting the revolutions that occur between the end of the traverse of the category code on track 444 and the end of traverse of the code on track 279; letting each revolution equal two; and using the odd-even information, ootained from track 155, to let the rst revolution equal one (instead of two) when the count ofthe stack is odd.

The operations performed to take this count will now be considered in detail.

When an active unload category code has completed a traverse of track 444, an R-pulse and output of and-gate 161 coincide in and-gate 168, which turns on liip-op 310 (FIG. 3D). The output of this flip-flop, indicating the start of a count, is applied to and-gate 311 in and-not gate 312.

Now when the stack has `an odd count, the revolution of memory drum 31, occurring when ip-tlop 310 is turned on, is counted as one, instead of two. More specically, an odd count of stack 46 is deduced from the absence of an even count, that is, when and-gate 160 fails to apply an output signal to inverter 314 (FIG. 3D) in and-not gate 315. The output of and-gate 168 is then passed through and-gate 316 to inverter 317 to inhibit and-gate 311 in and-not gate 312. Consequently, the R- pulse, generated `at the end of traverse of track 444 by the unload category code, is not transmitted through andgate 311 to advance binary counter 313. Instead, the output of and-gate 316 is branched to terminal 1 of flip-flop 318, which then applies a signal to one of nine and-gates 320.

Since flip-nop 310 is turned on, each succeeding R- pulse, representing a revolution of memory drum 3l, is passed through and-gate 311 to binary counter 313. Each time a pulse is applied to the counter, the value of the binary number recorded therein is advanced by two until the output of and-gate 301, which signals the end of traverse of the duplicate unload category code on track 279, is applied to terminal 0 of flip-flop 310, turning the latter of. Subsequent R-pulses can not pass through andgate 311 to advance binary counter 313, whose parallel outputs, together with the output of flip-flop 318, are applied to and-gates 320 to indicate the count of the number of letters in the completed stack 46.

Flip-flop 318 is turned off if, at the end of traverse of track 444 by another active unload category code, the outputs of and-gates 168, coincide in and-gate 319 and the output of and-gate 160, also applied to inverter 314, inhibits and-gate 316. In this way, a signal is applied to terminal 0, and not to terminal 1, of Hip-flop 318, turning the latter off, to register an even count.

Moreover, when the stack has an even count, the inhibited and-gate 316 applies no output to inverter 317 of and-not gate 312. The normal output of inverter 317 and the output of fiip-op 310, turned on as described above, enable and-gate 311 to pass the R-pulse, coincident with the end of traverse, to binary counter 313. During each succeeding revolution of memory drum 31, an R-pulse is generated and applied to the counter. Each pulse, applied to the counter, advances by two the value of the binary number recorded therein, until the output of and-gate 301 is applied to terminal 0 of flip-flop 310, turning the same off. Subsequent R-pulses can not pass through and-gate 311 to advance the counter, which with ip-op 318, then indicates the number of letters in the completed stack 46.

On the occurrence of the output of and-gate 301, which is branched in parallel to and-gates 320, the output of flip-flop 318 and the binary number in counter 313 are passed through the and-gates to 9-bit register 308. When, as noted above, and-gate 28S is enabled by the output of flip-flop 302, the same output enables and-gate 307 through which the information in register 308 is then transmitted in serial form to the next process machine, not shown, which may be an automatic labeller and bundler, or to a statistical accounting machine.

In this way, the active unload category co-de and count are synchronous with the end of the related stack of letters. The latter -informati-on is transferred to the next stack-processing machine at the time of exit of the end of the stack from the present sorting machine. More precisely, the zero letter of a completed stack and the start of transfer of the information are coincident with a position equal to one slot after the last slot of the present machine.

Operations using event schedule (FIGS. 5A and 5B) As described earlier, the read point V represents the presence of a trail bit in the first bit place of register 138 when the latter contains an active unload category code in its first comparing-position. The event schedule in FIGS. 5A and 5B illustrates a progressive accounting record for a sample group of successive tread points V of a single active unload category code. For the purpose of the following discussion, the advance of read point V is entirely dependent upon the physical advance (repositioning on track 444) of an active unload category code with its accompanying trail bit.

Some of the rules of operati-on, illustrated above, are summarized as follows:

(l) The fiducial mark X is advanced on track 279 one lbit position, the analog of one slot 24a, per revolution of memory drum 31.

(2) During each revolution of memory drum 31, both the odd-even mark and the read `point V are advanced one bit posit-ion, the analog orf slot 24a, except: (a) When an identity is `found in the rst comparing-position of register 138, the oddcven mark is advanced two bit positions; (b) When an identity is found in the second com paring-position of register 138, the read point V is advanced t'wo bit positions.

(3) When an active unload category code is in the first comparing-position in register 138 and the associated odd-even mark 0 and read point V are in line, the letter category code for the slot in line with the read point is not checked, but the letter category code for the slot ahead of the latter point is checked when the category code shifts to the second comparing-position of the register. (A letter category code is checked when it is compared with the active unload category code.)

(4) (a) When an active unload category code is in the first comparing-position in register 138 and the associated read point V is not in line with the odd-even mark O, the letter category code for the related slot aligned with this read point is checked; (b) if this letter category code identifies with the active unload category code, then in addition, the letter category code for the following slot will be checked in the second comparing-position.

(5) an even-count addition to a stack 46 is made at the point in the revolution of drum 31 where the related identity is found.

(6) An odd-count addition to a stack 46 is made at 180 of the revolution of drum 31 after the point where the related identity is found.

A typical example of operation will now be presented with tlhe assistance of the above rules and the timing schedule illustrated in FIGS. 5A, 5B. At the start of operation, the letters of the pertinent .active unload catteygorfy code, shown dotted in FIG. 5B, are positioned in the slots 24a, selected at random., in the figure. Again, at the start of operation, the associated fiducial mark X, odd-even mark O and trail bit in tracks 279, 155 and 144, respectively, are in line at the read point V. The active unload category in this example is chosen to be the direct category RNY.

It is noted that in FIG. 5B the length of each letter slot 24a is illustrated as equal to the length of a bit place on memory drum 31, so that the sequence of the slot numbers pre-recorded on tracks 204 can be aligned with a matching sequence of progressively designated letter slots. In this figurative relationship, with conveyor belt 41 shown traversing the stationary letter slots 24a from left to right, the drum traverses any structurally associated fixed point, such as a read head, from right to left. In the depiction of the progress of read point V, Ithe oddeven mark 0 is recorded either on line or one bit place to the left.

At the extent of progress depicted in FIGS. 5A, 5B, the letters represented las dotted lines have been discharged to conveyor 'belt 41. Each letter category code RNY in tracks 223, associated with a discharged letter, has been erased from the tracks and is shown in thin black lines. The odd-even mark, unload category code and duplicate unload category code are written on tracks 155, 444 and 279, respectively, in the manner shown in FIG. 5B.

Starting the example at slot O, since the read point V and the odd-even mark O are in line, comparison is blocked at the first comparing-position of register 138, and the letter category code for slot 1 is compared with the active unload category code RNY when the latter is in the second comparing-position of the register (Rule 3). Since this slot does not contain a letter in the unload category, identities are not found and the odd-even mark and read point are advanced one `bit position or one slot (Rule 2).

The fiducial mark is also advanced one slot (Rule l). In fact, mhe fiducia] mark X is advanced one slot during each revolution of memory drum 31. This is indicated in FIG. 5B an-d will be understood in the discussion below.

After revolution l, since the read point V and the oddeven mark 0 are still in line, but now at slot 1 where a comparison is now blocked, the letter category code for slot 2 is compared with the active unload category code RNY in accord with Rule 3. (More precisely, the comparison, in this case, blocked at one revolution rplus one bit occurs at one revolution plus two bits.) Because slot 2 contains a letter in this category, `an identity is found in the second comparing-position of register 138, and the first letter in stack 46, an odd-count addition, is discharged to conveyor belt 41 during revolution 2 (Rule 6). The odd-even mark O is advanced one slot `and the read point V is advanced two slots (Rules 2 and 2b).

After revolution 2, a comparison is permitted at the read point, now in line with slot 3, for the reason that the odd-even mark O and the read point are not in line (Rule 4a). Slot 3 does not hold a letter rin the unload category code; therefore, an identity is not kfound in the first comparing-position. The read point and odd-even mark are then advanced one slot (Rule 2).

After revolutions 3 and 4, slots 4 and 5, respectively, are yfound empty; and during each following revolution, the read point and odd-even mark are advanced one slot.

After revolution 5, the read point V is in line with slot 6; the odd-even mark 0 is still not in line at this point, so a comparison is permitted (Rule 4a). Since slot 6 contains a letter in the unload category, an identity is found in the first comparing-position in register 138. The letter category code for slot 7 is then compared with the unload category code in the second comparingw position (Rule 4b). Identities are found in each comparingposition, and consequently, the letter in slot 6, an even-count addition, is discharged to the stack 46 immediately, while the letter in slot 7, an oddount addition, Iis discharged during revolution 6 (Rules 5, 6), and stack 46 then contains three letters. The odd-even mark O is advanced two slots (Rule 2a); the read point V is advanced two slots (Rule 2b) during revolution 6.

After each of the revolutions 6 to 12, a respective one of the slots 8 to 14 is checked; and since each slot is empty, the read point and odd-even mark are advanced one slot per revolution. This is in accord with Rule 2.

After revolution 13, the read point V is in line with slot 15; and the odd-even mark 0 is not in line with the read point. In accord with Rule 4a, the category code for the letter in slot 15 is compared in the first comparing-position of register 138 with the unload category code. (This comparison is made at revolution 13 plus fifteen bits.) An identity is found, and consequently, the letter category code for slot 16 is compared with the unload category code in the second comparing-position of the register (Rule 4b). Because identities are found in the first and second comparing-positions, the letter in slot 15, an even-count addition, is discharged at the read point (Rule 5), while the letter in slot 16, an odd-count addition, is discharged half-a-revolution of drum 31 thereafter (Rule 6). Because identities are found in the first and second comparing positions, the odd-even mark O is advanced two slots (Rule 2a) and the read point V is advanced two slots (Rule 2b).

After revolution 14, the read point V is in line with slot 17, while the odd-even mark O is not. Thus, slot 17 is checked, and since it contains a letter in the category code, slot 18 is also checked (Rules 4a, 4b). Since the latter slot is empty, the read point V is advanced one slot and since a letter is identified in slot 17, the odd-even 2.1 mark O is advanced two slots (Rules 2, 2a). The letter in slot 17, an even-count addition, is discharged at the former read point (Rule 5) and the stack contains six letters.

After revolution l5, the odd-even mark O and the read point V are in line; consequently slot 18 is skipped and 19 is checked (Rule 3). The latter slot is found empty and the mark and point are each advanced one slot (Rule 2).

After revolution 16, the odd-even mark and read point are still in line at slot 19 which is skipped, but slot 20 is checked (Rule 3) and contains a letter in the unload category. The read point is therefore advanced two slots, and the odd-even mark, one slot (Rules 2b, 2). The letter in slot 2t) is an odd-count addition and is released to the stack half-a-revolution of drum 31 after the point at which the identities are found. The stack comprises seven letters and the odd-even mark, having been set out-of-line with the read point, reflects the odd condition.

After each of the revolutions 17, 18, and 19, a respective one of the slots 21, 22 and 23 is checked; and because each slot is found empty, the odd-even mark and read point are each advanced one slot (Rule 2). At twentyfour bit places after revolution 20, slot 24 is checked at the read point. Since the unload catego-ry code is identiied, the letter in slot 24 is released at this point as an even-count addition to the stack, and the letter category code for slot 25 is checked in the second comparing-position.

What is claimed is:

l. A stack-forming synchronizer for articles, each associated with one of a plurality of article category codes and each positioned in a respective one of a plurality of slots arranged in a sequence, comprising:

first storing means containing said article category codes, each in a code position related to a respective one of said slots, second storing means having a plurality of code positions, each related to a respective one of said slots,

means for recording at least one unload category code in one of the code positions in said second storing means,

first comparing means having a first and second comparing-position, means for transferring said unload category code from said second storing means to the first comparing-position and then to the second comparing-position, the first comparing-position being associated with the slot related to the code position from which the unload category code was transferred and the second comparing-position ybeing associated with the next slot occurring in said sequence of slots, second comparing means, first control means for selectively applying either the output of one of the comparing-positions or for applying the output of the first and second comparingposition in sequence to said second comparing means,

means for sequentially transferring to said second comparing means the article category codes in said first storing means related to the slots associated with the first and second comparing-position, respectively,

means for generating an output signal when an identity is found in the second comparing means,

means responsive to each output signal for releasing the article in the slot related to the article category code being applied to said second comparing means when the output signal is generated, and

second control means for re-recording the unload category code in said second storing means with a selected advance in code position.

2. The stack-forming synchronizer set forth in claim 2 wherein said first control means comprises:

means for generating an output signal dependent upon whether the count of the articles released from the slots is odd or even, and

means responsive to said output signal for selectively applying either the output of one of the comparingpositions or for applying the output of the rst and second comparing-position in sequence to said second comparing means. 3. The stack-forming synchronizer set forth in claim 2 wherein said first control means comprises:

signal generating means for providing a count signal dependent upon whether the count of articles released from the slots is odd or even, means responsive to the coincidence of said count signal and the presence of an unload category code in said first comparing-position for generating a first gating signal, means responsive to the coincidence of an unload category code in said first comparing-position and an output signal of said second comparing means for providing a second gating signal, means responsive to the absence of said first gating signal for applying the unload category code in said first comparing-position to the second comparing means, and means responsive to either the first or second gating signal for applying the unload category code in the second comparing-position to the second comparing means. 4. The stack-forming synchronizer set forth in claim 3 wherein said signal generating means comprises:

count-storage means having a plurality of code positions arranged in a desired sequence, means for generating an odd-even signal and for recording the same in one of said code positions, means responsive to an output signal generated by said second comparing means and the presence of the unload category code in said first comparing-position for advancing said odd-even signal a selected number of code positions in said sequence, means responsive to the absence of an output signal generated by said second comparing means when said unload category code is in the first comparingposition for advancing the odd-even signal at least one code position in said sequence, means for reading said odd-even signal out of said count-storage means, and means responsive to said odd-even signal for generating a count signal. 5. The stack-forming synchronizer set forth in claim 4 wherein said second control means comprises:

means responsive to an output signal generated by said second comparing means and the presence of the unload category code in said second comparing-position for advancing the latter code a predetermined number of code positions in said second storing means, and means responsive to the absence of an output signal generated by said second comparing means when the unload category code is in the second comparingposition for advancing the latter code at lcast one code position in said second storing means. 6. The stack-forming synchronizer set forth in claim 1 including:

a conveyor belt positioned beneath said slots, means for moving said belt at a speed such that in a predetermined time interval a reference point on the belt is advanced substantially the width of one of said slots, means responsive to the output signal generated by said second comparing means when the unload category code is in one of the comparing-positions for discharging at substantially the occurrence of the output signal the article from the slot related to the article category code being applied to the second comparing means, and means responsive to the output signal generated by the second comparing means when the unload category 

1. A STACK-FORMING SYNCHRONIZER FOR ARTICLES, EACH ASSOCIATED WITH ONE OF A PLURALITY OF ARTICLE CATEGORY CODES AND EACH POSITIONED IN A RESPECTIVE ONE OF A PLURALITY OF SLOTS ARRANGED IN A SEQUENCE, COMPRISING: FIRST STORING MEANS CONTAINING SAID ARTICLE CATEGORY CODES, EACH IN A CODE POSITION RELATED TO A RESPECTIVE ONE OF SAID SLOTS, SECOND STORING MEANS HAVING A PLURALITY OF CODE POSITIONS, EACH RELATED TO A RESPECTIVE ONE OF SAID SLOTS, MEANS FOR RECORDING AT LEAST ONE UNLOAD CATEGORY CODE IN ONE OF THE CODE POSITIONS IN SAID SECOND STORING MEANS, FIRST COMPARING MEANS HAVING A FIRST AND SECOND COMPARING-POSITION, MEANS FOR TRANSFERRING SAID UNLOAD CATEGORY CODE FROM SAID SECOND STORING MEANS TO THE FIRST COMPARING-POSITION AND THEN TO THE SECOND COMPARING-POSITION, THE FIRST COMPARING-POSITION BEING ASSOCIATED WITH THE SLOT RELATED TO THE CODE POSITION FROM WHICH THE UNLOAD CATEGORY CODE WAS TRANSFERRED AND THE SECOND COMPARING-POSITION BEING ASSOCIATED WITH THE NEXT SLOT OCCURING IN SAID SEQUENCE OF SLOTS, SECOND COMPARING MEANS, 